I did not know about this product until I saw it used on This Old House to sheath a curved porch roof. It is plywood with the veneer grain all in the same direction. Very bendy stuff and it doesn't need to be super thin to get the bend.

Bendable plywood, also known as Curve-Ply, Flexply, Wacky Wood and Wiggle wood, bending plywood, is normally made out of hardwood imported veneers with the layers all running in one direction, this allows bend-ability to the panel and can be applied on a curved radius. Our stocked bending plywood is manufactured in the United States and distributed throughout the country.